KEV Intelligence

Vulnerability report

Exploited in the wild Confirmed confidence In CISA KEV

CVE-2021-34523

Microsoft Exchange Server Elevation of Privilege Vulnerability

Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23 · affected before 15.00.1497.015

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Severity
CVSS 9.0 · Critical
Confidence
Confirmed
Exploit status
Exploited in the wild
EPSS
100.0%
First observed
—
Last observed
—

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2021-34523 is an unauthenticated Microsoft Exchange Server Elevation of Privilege Vulnerability.

Is it exploited?

Yes. KEV Intelligence tracks this CVE as a known exploited vulnerability. Confidence is confirmed.

Who is affected?

Microsoft / Microsoft Exchange Server 2013 Cumulative Update 23 affected before 15.00.1497.015.

What should we do?

Prioritize remediation. Validate affected assets and apply vendor fixes on an accelerated timeline.

Overview

Microsoft Exchange Server Elevation of Privilege Vulnerability

Microsoft Exchange Server Elevation of Privilege Vulnerability

Vendor Product Affected Status
Microsoft Microsoft Exchange Server 2013 Cumulative Update 23 Before 15.00.1497.015 Affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 19 Before 15.01.2176.012 Affected
Microsoft Microsoft Exchange Server 2016 Cumulative Update 20 Before 15.01.2242.008 Affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 8 Before 15.02.0792.013 Affected
Microsoft Microsoft Exchange Server 2019 Cumulative Update 9 Before 15.02.0858.010 Affected
View vendor advisory (opens in new tab)
Published
14 Jul 2021
Exploitation Reported
03 Nov 2021
Attack vector
Local
Complexity
Low
Privileges
None
User interaction
None

Tags

microsoft malware metasploit cisa ransomware

CVE References

Exploitation evidence

Why KEV Intelligence marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

CISA

Recorded 03 Nov 2021

Independent exploitation attestation added to the KEV Intelligence record.

Used in malware

CISA

Recorded 03 Nov 2021

Malware families have been linked to exploitation of this CVE.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEV Intelligence Pro API.

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Source Added
CISA First 2021-11-03 00:00 UTC
CVE 2026-08-10 15:31 UTC

Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets
0
User-Agents
0

Raw values available in Pro and Enterprise.

Virtual patch status

No KEV Intelligence virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

Learn about virtual patches →

Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner Reference Detected
Metasploit https://github.com/rapid7/metasploit-framework/blob/master/modules/exploits/windows/http/exchange_proxyshell_rce.rb 28 Apr 2025

Risk and context

Severity, weaknesses, and research context

CVSS v3.1

9.0 Critical
CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

EPSS

100.0%

All CVSS Scores

CVSS v3.1 9.0 Critical

CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:C/C:H/I:H/A:N

CVSS v2.0 7.5 High

AV:N/AC:L/Au:N/C:P/I:P/A:P

Timeline

From disclosure to observed exploitation

  1. KEV confirmed by CVE

    Exploitation attested by an external source

  2. Metasploit module available

    Exploit module available

  3. Added to CISA KEV

    Listed in the CISA Known Exploited Vulnerabilities catalog

  4. First public exploitation report

    Exploit observed in malware

  5. CVE published

    Vulnerability disclosed publicly

  6. CVE ID reserved

    Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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  • Evidence confidence and provenance
  • First-party sensor telemetry
  • PoC and scanner references
  • Affected versions and enrichment
  • Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2021-34523

Free JSON includes basic KEV fields 
{
  "cve_id": "CVE-2021-34523",
  "confidence": "Confirmed",
  "cvss_score": 9.0,
  "cvss_estimated": false,
  "epss_score": 0.9999,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": false
  },
  "sensor_telemetry": { "attempts": 0, "sensors": 0 }
}

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